Conventionally, in an imaging device such as a digital camera, with advance in a high performance of a lens barrel having a zoom lens function capable of changing a focal distance, or miniaturization of the imaging device according to the user's demand, there has been increasingly used a lens barrel in which a plurality of lens groups is collapsed when photographing is not carried out. Furthermore, because of the demand for not only simple reduction in dimension, but also further reduction in thickness, it is now important to reduce the thickness of the lens barrel in a collapsed position to the maximum extent.
As a technology to cope with the demand for reduction in thickness of the lens barrel, there has been used a lens barrel in which a lens cylinder retaining therein a plurality of lens groups is collapsed into the imaging device when not in use, and one of the lens groups is retracted out of an optical axis of the lens groups when the lens groups are collapsed.
A technology for retracting one of lens groups out of an optical axis is disclosed in, for example, JP 2003-315861A (Patent Document 1) and JP 2003-149723A (Patent Document 2). According to the structure disclosed in each of the Patent Documents 1 and 2, a mechanism is employed wherein an optical axis of a lens group retained by a retractable lens retaining frame is estranged from an optical axis of other lens group when the lens groups are collapsed and the optical axis of the lens group of the retractable lens retaining frame is made to coincide with the optical axis of other lens group when the photographing is being carried out. Since one of a plurality of lens groups disposed on the optical axis is retracted out of the optical axis when the lens groups are collapsed, the entire dimension of the lens barrel in a direction of the optical axis can be reduced, so that the thickness of the imaging device is reduced.
Note that, in the structure disclosed in Patent Documents 1 and 2, the lens retracted out of the optical axis is actually positioned within a lens cylinder provided in the lens barrel to retain therein the lens groups, even after the lens is retracted.
However, according to a structure of a conventional technology such as those disclosed in the Patent Documents 1 and 2, there has been a problem that it is difficult to accurately grasp a change in positions of the retractable lens retaining frame when the optical axis of the lens group retained by the retractable lens retaining frame is made to coincide with or estranged from the optical axis of other lens group in a transition from a collapsed state to a photographing state or from the photographing state to the collapsed state. There has been also a problem that it is difficult to accurately grasp displacement of the retractable lens retaining frame in an optical axis direction coaxial with the optical axis of other lens group when the photographing is being carried out. Further disadvantage of the conventional technology is that a mechanism for detecting the position of the retractable lens retaining frame in a direction estranging from the optical axis of other lens group and/or a mechanism for detecting the position of the retractable lens retaining frame in the optical axis direction coaxial with the optical axis of other lens group, become complicated.